Multiturn rotary encoder with multiple code carriers coupled by a reduction gear

ABSTRACT

A multi-turn rotary encoder that includes a first code carrier connected with an input shaft, a scanning device that scans the first code carrier and generates an absolute position of the input shaft within one revolution, and a digital code word is present at an output of the scanning device and a second code carrier for measuring the number of revolutions of the input shaft. A reduction gear is arranged between and coupled to the first and second code carriers. The second code carrier includes a magnetic body with at least one north and south pole and a substrate with a spatial arrangement of sensor elements integrated therein, which are sensitive to magnetic fields, is associated with the magnetic body. An evaluation circuit integrated into the substrate, wherein scanning signals, which are phase-shifted with respect to each other, from the sensor elements are supplied, and that the evaluation circuit combines the scanning signals in such a way that a second digital code word is present serially or in parallel at an output of the evaluation circuit. A combination logical device, which is supplied with the first and second digital code words and which forms a resultant multi-digit code word therefrom.

Applicants claim, under 35 U.S.C. § 119, the benefit of priority of thefiling date of May 6, 1998 of a German patent application, copyattached, Serial Number 198 20 014.5, filed on the aforementioned date,the entire contents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

It is necessary in many cases to absolutely determine the position of ashaft within one revolution, as well as the number of revolutions.Multi-turn rotary encoders are employed for this purpose, such as thosedescribed in EP 0 715 151 B1 and DE 42 20 502 C1. EP 0 715 151 B1corresponds to U.S. Pat. No. 5,734,266, the entire contents of which areincorporated herein by reference.

2. Description of the Related Art

The multi-turn rotary encoder in accordance with EP 0 715 151 B 1 isdescribed on page 9 of the HEIDENHAIN Company Prospectus: Code-Drehgeber[Rotary Encoder], April 1997. Several code disks are connected with eachother by a gear for the detection and differentiation of a plurality ofrevolutions of a shaft. Each code disk includes several code tracks withalternatingly arranged north and south poles. The code tracks aredifferently divided, for example, the coarsest one has only one northand south pole each, the next finer track has two north and south poleseach, and the finest track has eight north and south poles each. Thecode tracks are scanned by Hall sensors. An absolute multi-digit codeword is formed by the combination of the scanning signals of all Hallsensors, which indicates the absolute angular position of the code disk.

It is disadvantageous in connection with this multi-turn rotary encoderthat a code disk with several code tracks must be used in order togenerate a multi-digit code word.

In the multi-turn rotary encoder in accordance with DE 42 20 502 C1several code disks are also respectively connected with each other bymeans of a reduction gear. Each code disk includes a magnetic drum witha single north and south pole. Two Hall sensors, which are arrangedoffset from each other by 90°, are provided on the circumference of themagnetic drum. The magnetic field of the magnetic drum, which passesthrough the Hall sensors, is radially oriented. An analog sine andcosine signal is generated in one revolution of the magnetic drum. Theanalog sine and cosine signals of all code disks are fed to anevaluation unit, which forms the multi-digit code word, which in turnindicates the absolute angular position of the code disk over severalrevolutions.

It is disadvantageous here that it is necessary to mount the Hallsensors individually on a plate.

SUMMARY OF THE INVENTION

An advantage and object of the present invention is based on creating amulti-turn rotary encoder which is simply constructed and can bemanufactured cost-effectively.

This advantage and object is attained by a multi-turn rotary encoderthat includes a first code carrier connected with an input shaft, ascanning device that scans the first code carrier and generates anabsolute position of the input shaft within one revolution, and adigital code word is present at an output of the scanning device and asecond code carrier for measuring the number of revolutions of the inputshaft. A reduction gear is arranged between and coupled to the first andsecond code carriers. The second code carrier includes a magnetic bodywith at least one north and south pole and a substrate with a spatialarrangement of sensor elements integrated therein, which are sensitiveto magnetic fields, is associated with the magnetic body. An evaluationcircuit integrated into the substrate, wherein scanning signals, whichare phase-shifted with respect to each other, from the sensor elementsare supplied, and that the evaluation circuit combines the scanningsignals in such a way that a second digital code word is presentserially or in parallel at an output of the evaluation circuit. Acombination logical device, which is supplied with the first and seconddigital code words and which forms a resultant multi-digit code wordtherefrom.

An advantage and object of the present invention reside in that allsensor elements for scanning one or several code carriers are integratedin one chip and therefore are extremely accurately aligned with eachother and have the identical characteristics.

Exemplary embodiments of the invention are represented in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the principle of an embodiment of amulti-turn rotary encoder according to the present invention,

FIG. 2 shows a top view of a first embodiment of a rotatable codecarrier with a scanning device to be used with the multi-turn rotaryencoder of FIG. 1 according to the present invention,

FIG. 3 shows a top view of a second embodiment of a rotatable codecarrier with a scanning device to be used with the multi-turn rotaryencoder of FIG. 1 according to the present invention,

FIG. 4 shows a top view of a third embodiment of a rotatable codecarrier with a scanning device to be used with the multi-turn rotaryencoder of FIG. 1 according to the present invention,

FIG. 5 shows a top view of a fourth embodiment of a rotatable codecarrier with a scanning device to be used with the multi-turn rotaryencoder of FIG. 1 according to the present invention,

FIG. 6 shows a top view of a first embodiment of a common scanningdevice for several code carriers to be used with the multi-turn rotaryencoder of FIG. 1 according to the present invention,

FIG. 7 shows a top view of a second embodiment of a code carrier whichcan be rotated, as well as displaced, in relation to a scanning deviceto be used with the multi-turn rotary encoder of FIG. 1 according to thepresent invention, and

FIG. 8 shows the code carrier in accordance with FIG. 7 in a furtherposition according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The principle of a multi-turn rotary encoder is represented in FIG. 1.It includes a single-turn element and a multi-turn element. Thesingle-turn element includes a code disk 1, which is directly coupledwith the input shaft 2 which is to be measured. The code disk 1 has acoding 3, which can be scanned in an opto-electrical, magnetic,capacitive or inductive manner in order to divide a revolution of theinput shaft 2 into a plurality of differentiable sectors. Usually thiscoding 3 is a multi-track Gray code, however, it can also be formed by asingle-track chain code. The coding 3 is scanned by a scanning device 4,so that a multi-digit code word C1 is present at the output of thesingle-turn element, which indicates the absolute position of the inputshaft 2 within a single revolution.

The multi-turn element is provided for detecting the number ofrevolutions of the input shaft 2. It includes at least one code carrier5.1, which is coupled with the input shaft 2 by a reduction gear 6. Aneightfold reduction has been selected in the example represented.

As shown in FIG. 1, it is particularly advantageous if one or morereduction gears 11 is/are connected downstream of the code carrier 5.1,by means of which one or more further code carriers 5.2 is/are driven ina geared-down manner. It is particularly advantageous if all codecarriers 5 of the multi-turn element are identically designed. Becauseof this it is possible to also design the corresponding scanning devices7.1, 7.2 identically, which simplifies stock keeping and considerablyreduces the purchase price.

Each code carrier 5, such as code carriers 5.1, 5.2, has a singledipole, i.e. a north and a south pole. The poles of a code carrier 5 arescanned by a scanning device 7, such as scanning devices 7.1, 7.2. Thescanning device 7 includes a semiconductor substrate, into which severalsensor elements 8, 9, which are sensitive to magnetic fields, have beenintegrated. This semiconductor substrate 7.3 is shown enlarged in FIG.2. In the simplest case, two sensor elements 8, 9 in the form of Hallsensors are integrated. In the example, the sensitive sensor facesextend vertically with respect to the substrate surface and are arrangedrotated with respect to each other at an angle α. For example, the Hallsensors 8, 9 have maximum sensitivity in the direction indicated by thetwo-headed arrow, but are insensitive to magnetic fields extendingparallel with their longer drawn-in sides. A rotating magnetic field isgenerated by the magnet of the code carrier 5 being rotated around theaxis of revolution D, whose field lines lie parallel with the substratesurface in the area of the Hall sensors 8, 9, but which change theirdirection with respect to this surface as a function of the angle ofrotation. Therefore each one of the Hall sensors 8, 9 provides an analogsinusoidal scanning signal per revolution of the magnet of the codecarrier 5. When the angle α=90°, the scanning signals are phase-shiftedwith respect to each other by 90°, and it is possible by means of knowninterpolation methods to differentiate between a plurality of absolutepositions from this within one revolution of the magnet of the codecarrier 5. The evaluation circuit 10 necessary for this is alsointegrated into the substrate 7.3. The evaluation circuit 10 links theanalog scanning signals from the Hall sensors 8, 9 in such a way, thatseveral digital signals of different periods are present at the outputand form a Gray code, for example, or that a multi-digit code word C2 isalready serially present at the output.

However, the arrangement of the Hall sensors 8, 9 can also be selectedin accordance with FIG. 3. The sensitive surface of the Hall sensors 8,9 extends parallel with the surface of the substrates 7.3, and theeffective magnetic field of the magnet of the code carrier 5 extendsvertically with respect to the substrate surface. This arrangement hasthe advantage that the Hall sensors 8, 9 can be arranged at theoutermost circumference of the substrate 7.3, from which a large angularresolution results. The space in the center of the substrate 7.3 can beoptimally utilized for the evaluation circuit 10.

The multi-digit code words C1, C2, C3 respectively formed in theindividual scanning devices 4, 7.1, 7.2, or the respectively formeddigital signals of differing periods, are fed to a combination logicaldevice 14, which forms a resultant multi-digit code word CR from themand passes it on to a follow-up electronic device.

In place of only two sensor elements 8, 9, it is possible in anadvantageous manner to integrate a plurality of sensor elements 8.0 to9.5 in the semiconductor substrate, each forming angles α of less than90° with each other. An example of this is represented in FIG. 4. Here,the semiconductor substrate is identified by 7.4, and the sensorelements in the form of Hall sensors by 8.0 to 9.5. The code carrier 5is again embodied as a dipole with a single north and south pole. Tocompensate eccentricities during the rotation of the code carrier 5around the axis of rotation D, the sensor elements 8.0 to 9.5 arearranged symmetrically with respect to the axis of rotation D. Eachsensor element 8.0 to 9.5 provides one sinusoidal scanning signal withone period per revolution of the magnet of the code carrier 5.

The two scanning signals required for interpolation, which are offset by90° with respect to each other, are obtained by the combination of thescanning signals from the sensor elements 8.0 to 9.5 in that therespective scanning signals of the sensor elements 8.0 to 9.5, which arespatially located opposite each other, are subtracted from each other.

In the example in accordance with FIG. 4 this means that the analogscanning signals from the sensor elements 8.0 to 8.7 lying within afirst sector of 180° are added to form a first sum signal, and theanalog scanning signals from the associated, oppositely located sensorelements 8.8 to 9.5 are added to form a second sum signal. Both sumsignals are switched to the difference circuit, wherein the resultant0°—signal is present at the output of the difference circuit. Thescanning signal which is phase-shifted by 90° with respect to this isgenerated in the same way by summing the scanning signals from thesensor elements 8.4 to 9.1 located in a second sector of 180°, in thatthe analog scanning signals from the sensor elements 8.4 to 9.1 areadded to form a third sum signal, and the analog scanning signals fromthe oppositely located sensor elements 9.2 to 8.3 are added to form afourth sum signal. Both sum signals are switched to the differencecircuit, wherein the resultant 90° signal is present at the output ofthe difference circuit. The second sector is spatially displaced by 90°with respect to the first sector.

The scanning signals, phase-shifted by 90° with respect to each other,generated in this way again have one period per revolution of the magnetof the code carrier 5, wherein harmonic waves and eccentricity errorsare compensated to a large extent by the combination of the scanningsignals. Therefore a particularly accurate absolute positiondetermination within one revolution of the magnet of the code carrier 5is possible by the interpolation of these two scanning signals.

The interpolation can be performed in a known manner by a resistancenetwork, by arctan calculation or by the evaluation of tables. Theinterpolation unit assigns a unique absolute position within a period toeach combination of amplitudes of the two resultant analog scanningsignals. For example, a division by 2⁵=32-fold can take place.

It is essential for the invention that the circuit elements required forthe described evaluation and generation of a multi-digit code word C2,C3 are integrated in the substrate 7.4. In FIGS. 4 and 5 this integratedevaluation circuit is schematically identified by the reference numeral10 and dashed lines.

In the example in accordance with FIG. 4, the magnet of the code carrier5 is a disk- or drum-shaped body. The Hall sensors 8.0 to 9.5 arearranged spatially distributed over the outer circumference, so thattheir sensitive surfaces are oriented parallel with the surface of thesubstrate 7.4 and are affected by a magnetic field, which is orientedvertically with respect to the substrate surface, of the magnet of thecode carrier 5. The effect of the magnetic field on the individualsensor elements 8.0 to 9.5 is a function of the instantaneous positionof rotation of the magnet of the code carrier 5. The evaluation unit 10arranged in the substrate surface—which for example is enclosed by thesensor elements 8.0 to 9.5—derives the absolute position from themagnetic field distribution. A memory is provided for this, in which theallocation of the sensor elements 8.0 to 9.5 to the angle value isstored. If it is found, for example, that the sensor elements 8.1, 8.2lie in the range of the maximum magnetic field, an angle value of 20° isput out. To determine the location of the instantaneous maximal magneticfield it is also possible to interpolate between two sensor elements.When evaluating the instantaneous magnetic field position, the sensorelements 8.1, 8.2 can be detected, which output maximum signals, or itis also possible to determine a position where a transition from maximalto minimal signals is present, in the example this would be the sensorelements 9.3, 9.4.

A further variation is represented in FIG. 5. In contrast to FIG. 4, thesensor elements 8.0 to 9.5 are arranged underneath the magnet 5. Theeffective magnetic field lies in the area of the dividing line betweenthe north and the south pole.

The sensor elements 8, 9 of several scanning devices 7 of the multi-turnelement can also be integrated in a common substrate 7.13. Examples ofthis are represented in FIGS. 6 to 8.

In accordance with FIG. 6, the code carriers 5.1, 5.2, each of which isdriven via a reduction gear 6, 11 in accordance with FIG. 1, are locatedin a common plane. The scanning devices 7.1 and 7.2 are integrated intoa common substrate 7.13. For this purpose a two-dimensional sensor arrayof sensor elements 8, 9, which are sensitive to magnetic fields, isformed in the substrate 7.13. In the example, the array includes fourlines (numbered 1-4) and eight columns (numbered 1-8) of individualelements. Only two of the elements 8, 9 have been provided withreference numerals for reasons of clarity. The absolute rotary positionof each magnet 5.1, 5.2 can be determined as described in connectionwith FIGS. 2 to 5. Alternatively to this there is the possibility ofdetermining the absolute position from the instantaneous magnetic fielddistribution of both code carriers 5.1, 5.2 on the sensor array 7.13 bylogical evaluation. One of ordinary skill would understand that suchlogical evaluation would include having a logic device generating a codeword that is representative of the absolute position based on theinstantaneous position of the magnets 5.1, 5.2. Such a logic device canbe in the form or a table structure that enables “if-then” decisions tobe performed. An example of an “if-then” decision would be—If the northpole of the magnet 5.1 rests above a sensor element positioned at row 2,column 2 and the north pole of the magnet 5.2 rests above a sensorelement positioned at row 2, column 6, then this corresponds to a presetcondition.

The reduced movement transfer between the two code carriers 5.1, 5.2 isnot limited to a rotary movement.

The reduction gears 6, 11 represented in FIG. 1 can also be combinedinto a common reduction gear, so that the code carrier 5 not onlyperforms a rotary movement around an axis of rotation D, but also afurther displacement movement, superimposed on the rotary movement, or afurther rotary movement in relation to the sensor array 7.13. Thisexample is schematically represented in FIGS. 7 and 8. Following arevolution of the code carrier 5, the code carrier 5 is displaced fromthe position represented in FIG. 7 into the position represented in FIG.8. The second reduction gear 11 simulates the superimposed movement, itcan be linear, rotatory or spiral-shaped. The superimposed movement cantake place continuously or in steps.

In the examples in accordance with FIGS. 4 to 8, the code divisionincludes the spatial distribution of the sensor elements. As explainedpreviously, the spatial distribution of the sensor elements is used asthe position information of the magnetic body. Here, an address, whichdefines the position information of the sensor element in relation tothe other sensor elements, and therefore the spatial distribution on thesemiconductor substrate, is assigned to each sensor element.

Interface components and output drivers can also be integrated into thesemiconductor substrate 7, 7.4, 7.13.

The drawings are basic representations and are not drawn to scale.Actually, the surface of a sensor element is approximately 0.2 mm times0.4 mm.

It is also possible to employ other magnetically sensitive sensorelements, such as magnetoresistive elements or flux gates, in place ofHall sensors.

The invention may be embodied in other forms than those specificallydisclosed herein without departing from its spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects only as illustrative and not restrictive, and the scope of theinvention is commensurate with the appended claims rather than theforegoing description.

We claim:
 1. A multi-turn rotary encoder, comprising: a first codecarrier connected with an input shaft; a scanning device that scans saidfirst code carrier and generates an absolute position of said inputshaft within one revolution, and a digital code word is present at anoutput of said scanning device; a second code carrier for measuring thenumber of revolutions of said input shaft; a reduction gear arrangedbetween and coupled to said first code carrier and said second codecarrier; said second code carrier comprises a magnetic body with atleast one north and south pole; a substrate with a spatial arrangementof sensor elements integrated therein, which are sensitive to magneticfields, is associated with said magnetic body; an evaluation circuitintegrated into said substrate, wherein scanning signals, which arephase-shifted with respect to each other, from said sensor elements aresupplied, and that said evaluation circuit combines said scanningsignals in such a way that a second digital code word is presentserially or in parallel at an output of said evaluation circuit; and acombination logical device, which is supplied with said first and seconddigital code words and which forms a resultant multi-digit code wordtherefrom.
 2. A multi-turn rotary encoder, comprising: a first codecarrier connected with an input shaft; a scanning device that scans saidfirst code carrier and generates an absolute position of said inputshaft within one revolution, and a digital code word is present at anoutput of said scanning device; a second code carrier for measuring thenumber of revolutions of said input shaft; a reduction gear arrangedbetween and coupled to said first code carrier and said second codecarrier; said second code carrier comprises a magnetic body with atleast one north and south pole; a substrate with a spatial arrangementof sensor elements integrated therein, which are sensitive to magneticfields, is associated with said magnetic body; an evaluation circuitintegrated into said substrate, wherein scanning signals, which arephase-shifted with respect to each other, from said sensor elements aresupplied, and that said evaluation circuit combines said scanningsignals in such a way that a second digital code word is presentserially or in parallel at an output of said evaluation circuit; acombination logical device, which is supplied with said first and seconddigital code words and which forms a resultant multi-digit code wordtherefrom; wherein said second code carrier comprises a magnetic bodywith only a single north and south pole, so that each of said sensorelements generates a periodic sinusoidal scanning signal per revolutionof said magnetic bodies.
 3. The multi-turn rotary encoder in accordancewith claim 2, further comprising a third code carrier, wherein saidsecond and third code carriers are driven at different reductions bysaid input shaft, and each of said second and third code carriers isscanned by corresponding first and second semiconductor substrates.
 4. Amulti-turn rotary encoder, comprising: a first code carrier connectedwith an input shaft; a scanning device that scans said first codecarrier and generates an absolute position of said input shaft withinone revolution, and a digital code word is present at an output of saidscanning device; a second code carrier for measuring the number ofrevolutions of said input shaft; a reduction gear arranged between andcoupled to said first code carrier and said second code carrier; saidsecond code carrier comprises a magnetic body with at least one northand south pole; a substrate with a spatial arrangement of sensorelements integrated therein, which are sensitive to magnetic fields, isassociated with said magnetic body; a third code carrier, wherein saidsecond and third code carriers are driven at different reductions bysaid input shaft, and each of said second and third code carriers isscanned by corresponding first and second semiconductor substrates; anevaluation circuit integrated into said substrate, wherein scanningsignals, which are phase-shifted with respect to each other, from saidsensor elements are supplied, and that said evaluation circuit combinessaid scanning signals in such a way that a second digital code word ispresent serially or in parallel at an output of said evaluation circuit;and a combination logical device, which is supplied with said first andsecond digital code words and which forms a resultant multi-digit codeword therefrom.
 5. The multi-turn rotary encoder in accordance withclaim 4, wherein said first and second semiconductor substrates areidentically designed.
 6. The multi-turn rotary encoder in accordancewith claim 4, wherein said second and third carriers comprises amagnetic body with a single north and south pole.
 7. A multi-turn rotaryencoder, comprising: a first code carrier connected with an input shaft;a scanning device that scans said first code carrier and generates anabsolute position of said input shaft within one revolution, and adigital code word is present at an output of said scanning device; asecond code carrier for measuring the number of revolutions of saidinput shaft; a reduction gear arranged between and coupled to said firstcode carrier and said second code carrier; said second code carriercomprises a magnetic body with at least one north and south pole; asubstrate with a spatial arrangement of sensor elements integratedtherein, which are sensitive to magnetic fields, is associated with saidmagnetic body and wherein said substrate comprises a semiconductor; anevaluation circuit integrated into said substrate, wherein scanningsignals, which are phase-shifted with respect to each other, from saidsensor elements are supplied, and that said evaluation circuit combinessaid scanning signals in such a way that a second digital code word ispresent serially or in parallel at an output of said evaluation circuit;and a combination logical device, which is supplied with said first andsecond digital code words and which forms a resultant multi-digit codeword therefrom.
 8. A multi-turn rotary encoder, comprising: a first codecarrier connected with an input shaft; a scanning device that scans saidfirst code carrier and generates an absolute position of said inputshaft within one revolution, and a digital code word is present at anoutput of said scanning device; a second code carrier for measuring thenumber of revolutions of said input shaft; a reduction gear arrangedbetween and coupled to said first code carrier and said second codecarrier; said second code carrier comprises a magnetic body with atleast one north and south pole; a substrate with a spatial arrangementof sensor elements integrated therein, which are sensitive to magneticfields, is associated with said magnetic body and wherein each of saidsensor elements comprises a Hall element; an evaluation circuitintegrated into said substrate, wherein scanning signals, which arephase-shifted with respect to each other, from said sensor elements aresupplied, and that said evaluation circuit combines said scanningsignals in such a way that a second digital code word is presentserially or in parallel at an output of said evaluation circuit; and acombination logical device, which is supplied with said first and seconddigital code words and which forms a resultant multi-digit code wordtherefrom.
 9. The multi-turn rotary encoder in accordance with claim 8,wherein said sensor elements form an array arrangement with n sensorelements, with n greater than or equal to four.
 10. The multi-turnrotary encoder in accordance with claim 6, wherein said sensor elementsare integrated into a common semiconductor substrate for scanning saidsecond and third code carriers.
 11. A multi-turn rotary encoder,comprising: a first code carrier connected with an input shaft; ascanning device that scans said first code carrier and generates anabsolute position of said input shaft within one revolution, and adigital code word is present at an output of said scanning device; asecond code carrier for measuring the number of revolutions of saidinput shaft; a reduction gear arranged between and coupled to said firstcode carrier and said second code carrier, wherein said reduction gearcauses said first code carrier to rotate about a direction of rotation,as well as a displacement along a displacement direction that issuperimposed on said rotation; said second code carrier comprises amagnetic body with at least one north and south pole; a substrate with aspatial arrangement of sensor elements integrated therein, which aresensitive to magnetic fields, is associated with said magnetic body; anevaluation circuit integrated into said substrate, wherein scanningsignals, which are phase-shifted with respect to each other, from saidsensor elements are supplied, and that said evaluation circuit combinessaid scanning signals in such a way that a second digital code word ispresent serially or in parallel at an output of said evaluation circuit;and a combination logical device, which is supplied with said first andsecond digital code words and which forms a resultant multi-digit codeword therefrom.
 12. The multi-turn rotary encoder in accordance withclaim 11, wherein said sensor elements are integrated two-dimensionallyin said direction of rotation, as well as in said displacementdirection, next to each other in a semiconductor substrate.